The present invention relates to a triboelectric charge application member for imparting or applying electrostatic charge to a toner for developing electrostatic images in electrophotography, electrostatic printing and the like, by triboelectric charging of the toner, which triboelectric charge application member here covers not only the carrier particles which impart electrostatic charge to a toner through triboelectrification for use in a two-component type developer, but also a toner transportation member which also impart electrostatic charge to a toner through contact therewith, while regulating the thickness of a toner layer. Examples of such a toner transportation member are a development sleeve and a doctor blade Thus, in this patent application, materials, compositions and members which impart electrostatic charge to toner particles for use in the above-mentioned fields through contact therewith are collectively referred to as the triboelectric charge application member.
Conventionally there are two types of methods of developing latent electrostatic images to visible toner images. In the first development method, a two-component type developer comprising a mixture of toner particles and carrier particles is used, and in the second development method, a one-component type developer consisting of toner particles free from carrier particles is used.
In the first development method, a mixture of toner particles and carrier particles is stirred so that the toner particles are triboelectrically charged to a polarity opposite to the polarity of the carrier particles. Latent electrostatic images are developed by the thus triboelectrically charged toner particles to visible toner images. In such two-component dry-type developers, finely-divided toner particles are electrostatically held on the surface of comparatively large carrier particles. With access of the toner particles to a latent electrostatic image, the toner particles are attracted to adhere to the latent electrostatic image and adhere thereto, so that the latent electrostatic image is developed to a visible toner image. The developer can be used in repetition with replenishment of new toner particles for consumed ones from time to time in the course of the development.
Therefore, it is necessary that the carrier particles be capable of triboelectrically charging toner particles to the desired polarity, with a sufficient charge quantity, and that the charge quantity and the polarity thereof be maintained for a sufficiently long period of time for use in practice. In a conventional developer, however, it is apt to occur that melted toner particles adhere to the surface of the carrier particles, for instance, by collision between the toner and carrier particles or mechanical collision between the toner and carrier particles and the developing apparatus or by the subsequent heat build-up while in use. Once such a phenomenon takes place, which is generally referred to as the "spent phenomenon", the electrostatic characteristics of the carrier particles deteriorate with time, eventually resulting in the necessity for replacement of the entire developer by a new developer.
In order to prevent the spent phenomenon, a variety of methods have been conventionally proposed in which the surface of the carrier particles is coated with a variety of resins. For example, carrier particles are coated with a resin such as styrene-methacrylate copolymer and styrene polymer. Such carrier particles are excellent in the electrostatic charging characteristics. However, since the critical surface energy of the carrier particles is so high that the spent phenomenon cannot be suppressed effectively.
In contrast, carrier particles coated with a tetrafluoroethylene polymer have a low surface energy, so that the spent phenomenon scarcely takes place in the carrier particles; however, the adhesiveness of the tetrafluoroethylene polymer itself is so poor that it is difficult to fix firmly the polymer to the core particle of the carrier. Thus, such tetrafluoroethylene-polymer-coated carrier particles are not suitable for use in practice.
The second development method using a one-component type developer is conventionally known, for example, as disclosed in U.S. Pat. No. 4,196,060 and U.S. Pat. No. 4,160,884. In this development method, a triboelectric charge application member, such as a blade for regulating the thickness of a toner layer, comes into firm contact with the toner particles, and by the heat generated in the course of the firm contact of triboelectric charge application member with the toner particles, the toner particles are apt to be fused and adhere to the charge application member.